U.S. patent number 5,366,368 [Application Number 07/960,649] was granted by the patent office on 1994-11-22 for multi-plunger manual transfer mold die.
This patent grant is currently assigned to Goldstar Electron Co., Ltd.. Invention is credited to Keun Y. Jang.
United States Patent |
5,366,368 |
Jang |
November 22, 1994 |
Multi-plunger manual transfer mold die
Abstract
A preheaterless manual transfer mold die for encapsulating
semiconductor elements in a process for packaging semiconductors.
The preheaterless manual transfer mold die includes a multi-plunger
assembly adapted for upward and downward movement to press the
resin. A tablet loader is inserted into an upper mold die in order
to charge tablets into plunger bushes of the upper mold die. After
charging, the loader is pulled out of the upper mold die. The upper
mold die receives the tablets from the tablet loader. The tablets
are pressed by the multi-plungers. A lower mold die, clamped to the
upper mold die, receives the resin tablets in a gel state from the
upper mold die and fills cavities of chases with the resin to mold
semiconductor elements.
Inventors: |
Jang; Keun Y.
(Kyungsangbook-Do, KR) |
Assignee: |
Goldstar Electron Co., Ltd.
(Choongchungbook-Do, KR)
|
Family
ID: |
19322209 |
Appl.
No.: |
07/960,649 |
Filed: |
October 14, 1992 |
Foreign Application Priority Data
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Nov 14, 1991 [KR] |
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19459/1991 |
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Current U.S.
Class: |
425/544; 425/588;
425/127; 264/328.5; 425/572; 264/328.8; 264/272.17; 425/129.1;
257/E23.124 |
Current CPC
Class: |
H01L
23/3107 (20130101); B29C 45/02 (20130101); H01L
2924/0002 (20130101); H01L 2924/0002 (20130101); H01L
2924/00 (20130101) |
Current International
Class: |
B29C
45/02 (20060101); H01L 23/31 (20060101); H01L
23/28 (20060101); B29L 045/00 () |
Field of
Search: |
;264/272.11,272.14,272.17,328.4,328.5,328.8
;425/126.1,127,129.1,544,572,588 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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59-225913 |
|
Dec 1984 |
|
JP |
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61-214439 |
|
Sep 1986 |
|
JP |
|
62-195135 |
|
Aug 1987 |
|
JP |
|
63-28616 |
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Feb 1988 |
|
JP |
|
63-82717 |
|
Apr 1988 |
|
JP |
|
2189182 |
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Oct 1987 |
|
GB |
|
Primary Examiner: Bushey; Charles S.
Attorney, Agent or Firm: Lowe, Price, LeBlanc &
Becker
Claims
What is claimed is:
1. A multi-plunger manual transfer mold die comprising:
a multi-plunger assembly, having a plurality of plungers, which is
lowered and raised by a press so as to press resin tablets;
a tablet loader for containing a plurality of tablets which is
inserted in an upper mold die to charge the tablets into a
plurality of plunger bushes of the upper mold die and then pulled
out of the upper mold die;
the upper mold die including means to receive the tablet loader and
to receive the tablets from the tablet loader so that the tablets
can be pressed by the plungers; and
a lower mold die which is to be clamped to the upper mold die and
then receives in cavities of chases thereof the resin from the
upper mold die to mold half-finished products mounted in the
chases;
wherein said multi-plunger assembly includes a retainer fixed to an
end of a connecting rod integrally formed with a press cylinder
rod, a plurality of plunger rods downwardly projected from the
retainer, and a plurality of plunger tips each welded to each of
ends of the plunger rods;
wherein said connecting rod is provided with a flange at a lower
end thereof, a connector is inserted on the connecting rod and
mounted on the flange, and screws are engaged with the retainer
through holes formed at the connector, thereby causing the
connecting rod to be coupled to the retainer; and
wherein said retainer is formed with a plurality of holes each
having an enlarged step portion and an upper threaded portion,
bushes are mounted in the enlarged portions of the holes
respectively, each of the plunger rods is inserted in the bush at a
head end thereof, and each of the upper threaded portions of the
holes is engaged with a fixing nut, thereby causing the plunger
rods to be coupled to the retainer.
2. A multi-plunger manual transfer mold die comprising:
a multi-plunger assembly, having a plurality of plungers, which is
lowered and raised by a press so as to press resin tablets;
a tablet loader for containing a plurality of tablets which is
inserted in an upper mold die to charge the tablets into a
plurality of plunger bushes of the upper mold die and then pulled
out of the upper mold die;
the upper mold die including means to receive the tablet loader and
to receive the tablets from the tablet loader so that the tablets
can be pressed by the plungers; and
a lower mold die which is to be clamped to the upper mold die and
then receives in cavities of chases thereof the resin from the
upper mold die to mold half-finished products mounted in the
chases;
wherein said tablet loader comprises:
a loader body formed with a plurality of tablet charging gates
corresponding to the plunder rods,
a plurality of guide bearings rotatably mounted on opposite sides
of the loader body by shoulder screws which are inserted in guide
rails of the upper mold die,
a slide cover formed with holes corresponding to the tablet
charging gates of the loader body on which the loader body
slides,
a boss support fixed to an end of the slide cover which is formed
with supporting holes each having an enlarged step portion,
bosses which are mounted in the enlarged step portions of the boss
support at a head ends thereof and engaged with the loader body at
a threaded end thereof,
springs inserted on the bosses and interposed between the boss
support and the loader body to bias the loader body, and
a handle fixed to another end of the loader body for inserting the
tablet loader into the upper mold die and pull the tablet loader
out of the upper mold die.
3. A multi-plunger manual transfer mold die comprising:
a multi-plunger assembly, having a plurality of plungers, which is
lowered and raised by a press so as to press resin tablets;
a tablet loader for containing a plurality of tablets which is
inserted in an upper mold die to charge the tablets into a
plurality of plunger bushes of the upper mold die and then pulled
out of the upper mold die;
the upper mold die including means to receive the tablet loader and
to receive the tablets from the tablet loader so that the tablets
can be pressed by the plungers; and
a lower mold die which is to be clamped to the upper mold die and
then receives in cavities of chases thereof the resin from the
upper mold die to mold half-finished products mounted in the
chases;
wherein said upper mold die comprises:
a top mold base provided with a top center block at a lower surface
thereof, the top mold base being formed with a plurality of through
holes corresponding to the plungers therethrough and downward
extending leader pins at corners of a lower surface thereof,
a first top riser block and a second top riser block, the first top
riser block being divided into a front part and a rear part which
are fixed to an end of an upper surface of the top mold base and
the second top riser block being an integral part which is fixed to
the other end of the upper surface of the top mold base,
front and rear top ejector plates which are mounted between the
first and second top riser blocks and moveable towards or away from
the top mold base along a top return pin and a top stud bolt fixed
to the top mold base,
front and rear top drive plates which are mounted on the front and
rear to ejector plates respectively and moveable towards or away
from the top mold base along the top return pin and the top stud
bolt fixed to the top mold base, the front and rear top drive
plates being formed at facing surfaces thereof with guide rails for
guiding movement of the tablet loader,
front and rear top clamp blocks, the front top clamp block being
mounted on the first top riser block and the front part of second
top riser block at opposite ends thereof and the rear top clamp
block being mounted on the first top riser block and the rear part
of second top riser block at opposite ends thereof; and
front and rear top insulation plates which are mounted on the front
and rear top clamp blocks respectively; and
wherein said top center block is formed with a plurality of slots
at an upper surface thereof and with a plurality of through holes
formed at the slots coinciding with the through holes at the top
mold base.
4. A multi-plunger manual transfer mold die comprising:
a multi-plunger assembly, having a plurality of plungers, which is
lowered and raised by a press so as to press resin tablets;
a tablet loader for containing a plurality of tablets which is
inserted in an upper mold die to charge the tablets into a
plurality of plunger bushes of the upper mold die and then pulled
out of the upper mold die;
the upper mold die including means to receive the tablet loader and
to receive the tablets from the tablet loader so that the tablets
can be pressed by the plungers; and
a lower mold die which is to be clamped to the upper mold die and
then receives in cavities of chases thereof the resin from the
upper mold die to mold half-finished products mounted in the
chases;
wherein said lower mold die comprises:
a lower mold base formed with guide holes for guiding the leader
pins of the upper mold die, wherein said lower mold base is clamped
to the upper mold die,
a bottom center block mounted on the lower mold base which is
formed at an upper surface thereof with a plurality of runners
corresponding to the plungers, the runners being in communication
with each other by gate grooves,
chases mounted on both sides of the bottom center block which have
a plurality of cavities being in communication with the gate
grooves,
bottom riser blocks mounted on opposite ends of a lower surface of
the bottom mold base,
a bottom ejector plate and a bottom drive plate disposed between
the bottom riser blocks, and
a bottom clamp block and a bottom insulation block mounted on lower
surfaces of the bottom riser blocks.
5. A multi-plunger manual transfer mold die according to claim 4,
wherein said bottom center block comprises:
the plurality of runners formed at the upper surface of the bottom
center block which corresponds to the plungers;
the gate grooves being in communication with the runners and the
chases through which resin introduced in the runners is injected
into the chases; and
protrusions provided in the runners each of which has a diameter
smaller than that of the runner.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a preheaterless manual transfer
mold die for encapsulating semiconductor elements in a
semiconductor packaging process, and more particularly to a
multi-plunger manual transfer mold die which is provided with a
multi-plunger assembly instead of one plunger and without a
preheater so as to reduce amount of resin used in encapsulation of
elements and the curing-time required to stabilize resin, thereby
promoting productivity of the mold die.
2. Description of the Prior Art
Referring to FIG. 1, there is shown a conventional manual transfer
mold die commonly used in the molding procedure in the process for
manufacturing semiconductor packages. As shown in the drawing, the
manual transfer mold die may be divided into two main groups, that
is, an upper mold die "T" and a lower mold die "B".
The upper mold die "T" comprises a top mold base 1 which is
provided with four leader pins 1a at four corners of lower surfaces
thereof and a through hole 1b at a center portion thereof, a top
center block 2 having a through hole coinciding with the through
hole 1b which is fixed to a lower surface of the top mold base 1,
top riser blocks 3 and 3' which are divided into front parts and
rear parts respectively and mounted on opposite ends of upper
surface of the top mold base 1, a top ejector plate 7 interposed
between the top riser block 3 and 3' and disposed on the top mold
base 1, a top drive plate 6 mounted on the top ejector plate 7, a
cylinder plunger bush (or pot) 9 which passes through the top drive
plate 6 and the top ejector plate 7 which has an inside hole
corresponding to the through hole 1b of the top mold base 1, a
plunger 8 adapted to be slidably inserted in the plunger bush 9 by
means of a press (not shown), a top return pin 10 fixed to an upper
surface of the top mold base 1 which passes through the top drive
plate 6 and the top ejector plate 7 and along which the top drive
plate 6 and the top ejector plate 7 are slidable, a stud bolt 13
passing through the top drive plate 6 and the top ejector plate 7
which is provided with a spring 14 and engaged with a washer and
cushion lock nut 15 at the upper end thereof, a top support pillar
11 mounted on the top drive plate 6, top insulation plates 5 and 5'
which are mounted on the front parts and the rear parts of the top
riser blocks 3 and 3' respectively, top clamping blocks 4 and 4'
which are mounted on the top insulation plates 5 and 5'
respectively, and a plurality of screws 12 for assembling the
above-mentioned components.
On the other hand, the lower mold die "B" comprises a bottom mold
base 21 which is formed with guide holes 21a in which the leader
pins 1a formed at the top mold base 1 of the upper mold die "T" are
slidably inserted, a bottom center block 22 mounted on the bottom
mold base 21 which is formed with a runner 22a and gates 22b at an
upper surface thereof, chases 23 which are mounted on both sides of
the center block 22 and have a plurality of cavities connected to
the gates 22b, bottom riser blocks 24 and 24' mounted on opposite
ends of a lower surface of the bottom mold base 21 respectively, a
bottom ejector plate 28 which is mounted under the bottom mold base
21 and spaced from the bottom riser block 24 and 24', a spring
inserted in a hole 28a formed at an upper surface of the bottom
ejector plate 28, a bottom drive plate 27 mounted under the bottom
ejector plate 28, a bottom return pin 32 fixed to the bottom drive
plate 27 which slideably passes through the bottom ejector plate 28
and has a stopper 33 at lower end thereof, a bottom insulation
plate 26 which is mounted on lower surfaces 24 and 24' and under
the bottom drive plate 27, a bottom clamp block 25 mounted under
the bottom insulation plate 26, a bottom support pillar 30 fixed to
the bottom drive plate 27 which is slidably inserted into a through
hole 28b of the bottom ejector plate 28, and a plurality of screws
for assembling the above-mentioned components.
An operation of the above known manual transfer mold die will be
described as follows.
First, preheated lead frames (not shown) are placed in the cavities
of the chases 23 mounted on both sides of the bottom center block
22 of the lower mold die "B". Thereafter, the upper and lower mold
dies "T" and "B" are clamped by means of the top and bottom clamp
blocks 4 and 25. Accordingly, the top center block 2 of the upper
mold die "T" is tightly closed to the bottom center block 22 of the
lower mold die "B" and the chases 23 mounted on both sides of the
bottom center block 22 so that the runner 22a of the bottom center
block 22, the gates 22b and the cavities of the chases 23 are
sealed.
Subsequently, a massive resin tablet (not shown) is preheated by a
high-frequency preheater (not shown) and then put into the plunger
bush 9 of the upper mold die "T".
Then, upon pushing a switch of molding press (not shown) related to
the plunger 8, the plunger 8 is lowered through the plunger bush 9
so that the resin tablet in the plunger bush 9 is injected into the
runner 22a of the bottom center block 22 through the through hole
1b of the top mold base 1. At this time, since the resin tablet is
normally preheated to a temperature of 85.degree.-95.degree. C. and
the mold die is heated to a temperature of 175.degree..+-.5.degree.
C., the resin tablet changes into gel and is injected into the
runner 22a. The resin tablet in a gel state is injected into the
chases 23 through the gates 22b to fill the cavities of the chases
23.
When the cavities in the chases 23 are completely filled with the
resin, the downward movement of the plunger 8 is stopped but the
pressurization of the plunger 8 is continuously maintained. Upon
being pressurized, the resin is cured. Although the curing time
required to cure resin is variable according to desired products,
it generally requires a time of 200-300 seconds to cure resin.
When the resin is completely cured, the plunger 8 is raised by the
molding press. Thereafter, as the upper mold die "T" is separated
from the lower mold die "B", the molded products are raised from
the chases 23 by a push pin (not shown) to be removed.
However, when the above-mentioned known manual transfer mold die
has a large number of cavities in the chases 23 (for example, the
mold die has generally 40-660 cavities), it requires a large amount
of resin to mold. Accordingly, resin tablets become large in size
because there are only one plunger 8 and one plunger bush 9.
Hence, resin tablets must be put in the plunger bush 9 after being
preheated in order to change the resin tablet into gel. Therefore,
a preheater must be used in order to preheat the resin tablets,
thereby increasing consumption of electric power and necessitating
additional space to establish the preheater.
In addition, since resin must be filled in a plurality of cavities
through only one runner 22a and then stabilized, it takes a long
curing time to stabilize the resin. Also, since the resin tablet
must be put in only one plunger bush 9, a large amount of resin
tablet must be consumed, thereby decreasing productivity.
Furthermore, since large air gaps are formed between the plunger
bush 9 and resin tablet, defects such as foam and porosity and wire
sweeping may occur.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above-described
problems occurring in the prior art and an object of the invention
is to provide a multi-plunger manual transfer mold die which has a
multi-plunger assembly so as to lessen amount of resin to be put in
the plunger bushes, thereby causing the curing time to be shortened
and productivity of semiconductor package molding processes to be
improved.
Another important object of the invention is a multi-plunger manual
transfer mold die which can carry out a molding process without
preheating the tablets by incorporating a multi-plunger system.
In accordance with the present invention, the objects mentioned
above can be accomplished by providing a multi-plunger manual
transfer mold die which presses resin tablets charged in an upper
mold die by means of multi- plungers so that the resin is injected
into cavities of chases of a lower mold die to mold objects in the
cavities. The multi-plunger manual transfer mold die includes: a
multi-plunger assembly having a plurality of plungers which are
adapted to be moved upward and downward by a press so as to press
resin; a tablet loader having a plurality of tablet charging gates
which is inserted in an upper mold die to charge tablets in the
tablet charging gates into a plurality of plunger bushes of the
upper mold die. The upper mold die also includes a top mold base
and a top center block mounted on a lower surface of the top mold
base which have a plurality of through holes corresponding to the
plungers which pass therethrough, a first top riser block being
divided into a front part and a rear part which are fixed to an end
of an upper surface of the top mold base and a second top riser
block being an integral part which is fixed to the other end of the
upper surface of the top mold base, front and rear top ejector
plates mounted between the first and second top riser blocks, front
and rear top drive plates mounted on the front and rear ejector
plates respectively which have, at facing surfaces thereof, guide
rails for guiding insertion an secession of the tablet loader, a
front top clamp block mounted on the first top riser block and the
front part of second top riser block at opposite ends thereof and a
rear top clamp block mounted on the first top riser block and the
rear part of second top riser block at opposite ends thereof, and
front and rear top insulation plates mounted on the front and rear
top clamp blocks respectively; a lower mold die including a lower
mold base formed with guide holes for guiding the upper mold die
which is to be clamped to the lower mold die, a bottom center block
mounted on the lower mold base which is formed at an upper surface
thereof with a plurality of runners being in communication with
each other by gate grooves, chases mounted on both sides of the
bottom center block which have a plurality of cavities being in
communication with the gate grooves, bottom riser blocks mounted on
opposite ends of a lower surface of the bottom mold base, a bottom
ejector plate and a bottom drive plate disposed between the bottom
riser blocks, and a bottom clamp block and a bottom insulation
block mounted on lower surfaces of the bottom riser blocks.
In operation of the multi-plunger manual transfer mold die
according to the invention, the upper mold is first clamped to the
lower mold die. The tablet loader containing tablets is inserted
into the upper mold die along the guide rails to charge the tablets
into the through holes of the top mold base and then pulled out of
the upper mold die. Thereafter, upon operating the press, the
multi-plungers press the tablets introduced in the through holes of
the top mold base. Accordingly, the tablets change into gel and are
injected into the runners of the bottom center block of the lower
mold die. The resin in gel state fills in the cavities of the
chases through the gate grooves. Subsequently, the resin in the
cavities is cured by pressurization of the multi-plungers for a
certain duration, thereby completing the molding process.
Therefore, since a plurality of small sized tablets are
simultaneously charged into the upper mold die and then injected
into the cavities through a plurality of runners, there is no need
to preheat the tablets and the time required to cure the resin is
shortened.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other objects, features and advantages of the invention
will become more apparent upon a reading of the following detailed
specification and drawings, in which:
FIG. 1 is an exploded perspective view showing a known manual
transfer mold die;
FIG. 2 is an exploded perspective view showing a multi-plunger
manual transfer mold die according to the present invention;
FIG. 3 is the vertical sectional view of a multi-plunger assembly
in FIG. 2;
FIG. 4 is a top plan view showing a tablet loader according to the
invention;
FIG. 5 is a vertical sectional view of the tablet loader in FIG.
4;
FIG. 6 is a perspective view showing a top center block according
to the invention; and
FIG. 7 is a perspective view showing a bottom center block
according to the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A multi-plunger manual transfer mold die according to the present
invention will now be described by referring to FIGS. 2 to 7 in the
accompanying drawings.
Referring to FIG. 2, there is shown a multi-plunger manual transfer
mold die according to the invention which is in exploded view. As
shown in the drawing, the multi-plunger manual transfer mold die
comprises a multi-plunger assembly 70 having a plurality of
plungers, an upper mold die "T" which is adapted to receive a
plurality of tablets which are simultaneously pressed by the
plungers of the multi-plunger assembly, a lower mold die "B",
formed with runners corresponding to the plungers, to which resin
is introduced from the upper mold die "T" to mold objects in the
cavities thereof, and a tablet loader 40 for charging a plurality
of tablets into the upper mold die "T".
In the upper mold die "T", a top center block 50 is welded to a
lower surface of a top mold base 1 and leader pins 1a are fixed to
four corners of a lower surface of the top mold base 1. The top
mold base 1 and the top center block 50 are formed with through
holes corresponding to the plungers and plunger bushes are inserted
in the through holes respectively.
A top riser block 3 is divided into a front part and a rear part
and fixed to an end of an upper surface of the top mold base 1 and
another integral top riser block 3' is fixed to the other end of
the top mold base 1.
A top ejector plate 7 and a top drive plate 6 are mounted on the
top mold base 1 and between the top riser blocks 3 and 3' which are
upward and downward movable along a top return pin 10 and a top
stud bolt 13. The top drive plate 6 is divided into a front top
drive plate 6a and a rear top drive plate 6b and the top ejector
plate 7 is divided into a front top ejector plate 7a and a rear top
ejector plate 7b, respectively.
The front and rear top drive plates 6a and 6b are formed with inner
facing side surfaces thereof having guide rails 6c for guiding
insertion/secession of the tablet loader 40. Top clamp blocks 4a
and 4b and top insulation plates 5a and 5b are divided into front
parts 4a and 5a and rear parts 4b and 5b respectively and mounted
on the top riser blocks 3 and 3'.
On the other hand, in the lower mold die "B", guide holes 21a are
formed at four corners of a lower mold base 21 to guide the reader
pins 1a fixed to the top mold base 1 of the upper mold die "T" and
a bottom center block 60 having a plurality of runners
corresponding to the plungers is welded to an upper surface of the
lower mold base 21, the runners being connected to each other by
gate grooves 64 (see FIG. 7). Chases having a plurality of cavities
connected to the gate grooves 64 are mounted on both sides of the
bottom center block 60.
Under the bottom mold base 21 is mounted bottom riser blocks 24 and
24', a bottom ejector plate 28, a bottom drive plate 27, a bottom
clamp block 26 and a bottom insulation block 25.
Referring to FIG. 3, there is shown a section of a multi-plunger
assembly according to the invention. The multi-plunger assembly 70
comprises a retainer 74 fixed to a lower end of a connecting rod 72
integrally formed with a press cylinder rod 71, a plurality of
plunger rods 77 protruding downward from the retainer 74, and
plunger tips 79 welded to ends of the plunger rods 77.
The connecting rod 72 is formed with a flange at a lower end
thereof. A connector 73 is inserted on the connecting rod 72 and
mounted on the flange of the connecting rod 72. The connector 73 is
coupled to the retainer 74 by means of screws 73' so that the
connecting rod 72 is fixedly mounted on the retainer 74.
The retainer 74 is formed with a plurality of holes 75, each of the
holes having an enlarged step portion. A guide bush 76 is mounted
in each of holes 75 and placed on the step portion. The plunger
rods 77 are inserted in the holes 75 through the guide bush 76 such
that heads of the plunger rods 77 are placed on the step portions.
The holes 75 are formed with threaded portions at upper ends
thereof and the threaded portions are engaged with fixing nuts.
Referring to FIGS. 4 and 5, there are shown a tablet loader
according to the invention. As shown in the drawings, the tablet
loader 40 comprises a loader body 41 having a plurality of tablet
charging gates 44 and having a plurality of guide bearing 42
rotatably mounted on both sides of the loader body 41 by shoulder
screws 43 which are to be inserted into the guide rails 6c formed
at the upper mold die "T", a boss support 48 having supporting
holes 48', each of the supporting holes 48' having an enlarged step
portion, bosses 45 which are mounted in the supporting holes 48' at
head ends thereof and engaged with an end of the loader body 41 at
threaded ends 45a thereof, springs 46 which are interposed between
the boss support 48 and the loader body 41 and inserted on the
bosses 45 to bias the loader body 41 rightward in the drawings, a
slide cover 49 which is connected to the boss support 48 by a
plurality of screws 49' and has holes 49a corresponding to the
tablet charging gates 44, and a handle 47 fixed to the other end of
the loader body 41 which is adapted to insert the tablet loader 40
into the upper mold die "T" and pull the tablet loader out of the
upper mold die.
Referring to FIG. 6, there is shown a top center block according to
the invention. The top center block 50 comprises a block body 51, a
plurality of slots 52 formed at the upper surface of the block body
51, and a plurality of through holes 53 and 53' formed at the slots
52 which correspond to the plungers 77. Plunger bushes (not shown)
are inserted into the through holes 53 and 53'. Flanges of the
plunger bushes are placed on the slots 52 so that the plunger
bushes are maintained in the through holes 53 and 53'. Although the
slots 52 may be formed into a circular shape, the slots 52 shown in
the drawing are formed into a shape which can be machined
easily.
Referring to FIG. 7, there is shown a bottom center block according
to the invention. The surface of block body 61, of the top center
block 60, which is to be close to a lower surface of the top center
block 50, is formed with a plurality of circular grooves or runners
62. The runners 62 are in communication with each other by means of
gate grooves 64. The runners 62 are provided with protrusions 63
having diameters smaller than those of the runners 62,
respectively. The protrusions 63 have been generally used in order
to reduce consumption of resin.
Operation of the multi-plunger manual transfer mold die according
to the present invention will be described hereinafter.
First, desired objects to be molded (for example, a semiconductor
chip connected to a lead frame) are put in the chases 23 of the
lower mold die "B" separated from the upper mold die "T". In this
case, a plurality of preheated lead frames are mounted on a loading
fixture and put in the chases 23 so that the lead frames are
precisely disposed by location pins of the chases 23 (not shown,
usually 3EA/FRAME), respectively.
Thereafter, the upper mold die "T" is clamped to the lower mold die
"B". Certain sized tablets are put in the tablet charging gates 44
of the tablet loader 40 respectively. The tablet loader 40
containing the tablets is pushed into the upper mold die "T" along
the guide rails 6c of the top drive plates 6a and 6b. After the
tablet loader 40 has been pushed completely and stopped at a
certain position, upon further pushing of the handle 47 of the
tablet loader 40, the tablet loader body 41 is moved toward the
boss support 48 against the springs 46. As the tablet loader body
41 is moved to the boss support 48, the tablet charging gates 44 of
the loader body 41 coincide with holes 49a of the slide cover 49.
At this time, the tablets contained in the tablet charging gates 44
are dropped into the through holes of the top mold base 1. That is,
the slide cover 49 functions as a shutter for tablet.
After the tablets have been dropped, the tablet loader 40 is
manually pulled out of the upper mold die by an operator. Then,
upon operating a press, the multi-plunger assembly 70 is lowered so
that the plunger tips 79 welded to ends of the plunger rods 77 are
inserted into the through holes of the top mold base 1 to press the
tablets.
At this time, since the upper mold die was previously heated to a
temperature of about 175.degree. C., the relative small mass of the
tablets contained in the through holes of the top mold base 1
change into gel and are injected into the runners 64 of the bottom
center block 60 of the lower mold die "B".
On the other hand, since a prior manual transfer mold die uses a
relatively large massive tablet (for example, having a diameter in
a range of 48-58 mm) and only one plunger, the tablet must be
previously preheated to change into gel. However, since the
multi-plunger manual transfer mold die according to the invention
presses a plurality of tablets by a plurality of plungers, tablets
can be divided into relative small mass tablets (for example,
having a diameter of 24 mm) and charged into the mold die.
Therefore, the tablets can change easily into gel with the mold die
preheated to a temperature of 175.degree. C. and without procedure
for preheating tablets.
As the multi-plungers are further lowered, the resin in a gel state
fills the cavities of the chases 23 through the gate grooves 64.
When the plungers are lowered such that the resin is bulged to a
height of 2-3 mm above the runners 62, the resin is completely
filling the cavities and descent of the plungers is stopped but
pressurization of the plungers is maintained for a certain
duration.
In this case, it is important to reduce the amount of resin
remaining in the runners 62 and the gate grooves 64, namely to
reduce consumption of resin. Since total volume of the runners
according to the invention is smaller than that of the prior
runner, it is possible to reduce consumption of resin as compared
with the prior art. For a better understanding of the present
invention, lead frames having 14/16 leads were molded by the mold
die according to the invention and a prior mold die, both having
168 cavities. The mold die according to the invention consumed 192
g of resin but the prior mold die consumed 240 g of resin.
Accordingly, the multi-plunger manual transfer mold die according
to the invention can reduce consumption of resin by 10% compared
with a prior mold die.
While the above-mentioned pressurization of the plungers is
continuously maintained, the resin is cured. Although a time
required to cure resin may vary according to desired products, the
mold die according to the invention commonly requires a time of
60-100 sec to cure resin. Therefore, the curing time required in
the mold die according to the invention is substantially shortened
as compared with a prior mold die.
Thereafter, when curing of the resin is completed, the
multi-plunger assembly 30 is raised and then the upper mold die "T"
is separated from the lower mold die "B". Then, the molded products
(for example, semiconductor packages) are lifted out of the
cavities by push pins in the chases 23 and removed by an
operator.
As apparent from the above description of the invention, since the
multi-plunger manual transfer mold die uses small diameter of
tablets differently from a prior art, there is no necessity for
preheating tablets in order to change the tablets into gel.
Furthermore, since a preheater is not necessary for preheating, it
is possible to reduce the waste of electric power and space
occupied by the molding system.
Also, since air gaps between the plunger bushes and tablets are
small because the diameter of the plunger bushes is smaller than
the diameter of the prior plunger bush, foam, porosity and wire
sweeping are considerably reduced and also the waste of resin is
reduced.
Finally, since resin is filled in the cavities through a plurality
of runners and then cured, the time required to cure the resin is
shortened, thereby improving productivity.
Although the preferred embodiments of the invention have been
disclosed for illustrative purpose, those skilled in the art will
appreciate that various modifications, additions and substitutions
are possible, without departing from the scope and spirit of the
invention as disclosed in the accompanying claims.
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